Friday, April 26, 2013

Voltage Regulators Protector

People ceaselessly fail to remember that many voltage regulator ICs have an upper restrict (usually 35 V) on the input voltage they are able to deal with. That applies essentially to sorts with a fixed output voltage. Adjustable voltage regulators actually have a maximum voltage specification, in that case between the enter and output (commonly forty V). The enter voltage should as a result be limited to that stage in a fault situation through which the output is briefed. This circuit presentations a solution to enable such regulators for use in state of affairss with greater input voltages. Although the answer includes an extra three parts, it is easy and can also be constructed using usually available components.

The voltage throughout the regulator is restricted by using the mix of T1 and zener diode D1 to a price that lets the regulator to work properly with loads up to the most rated load. R1 professionalvides an enough operating present for D1 and the bias present for T1. It’s a excellent suggestion to use a Darlington kind for T1 to be able to maintain the worth of R1 reasonably excessive. The current thru D1 is simplest 10 mA with an enter voltage of 60 V. Naturally, we additionally measured what the circuit does when no load is connected. Surprisingly sufficient, the nominal output voltage of 5.02 V increased to best 5.10 V (with a 60-V input voltage). In our scans, we used a BDV65B for T1 and a value of 4.7 kΩ for R1.

If you are having a look to have to be sure that the circuit is really brief-circuit professionalof with an enter voltage of 60 V, you should use a transistor that is still within its safe working house at the maximum enter voltage with the brief circuit current of the regulator (which can exceed 2 A). The BDV65B and TIP142 do not meet this requirement. The maximum voltage for the BDV65B is actually 40 V, and for the TIP142 is 50 V. If the transistor spoils down, the regulator may even spoil down. We verified that experimentally. One risk is so as to add SOA professionaltection for T1, but that quantitys to professionaltecting the professionaltection. Another possibility is to chill out the requirements.

For that objective, R1 must provide enough current to ensure that T1 receives enough current in the event of a brief circuit to maintain the voltage across T1 decrease, however that doesn’t make various distinction in apply, and it additionally increases the minimal load. Besides that, it should be evident that adequate cooling for T1 and IC1 should be provided in maintaining with the load. Ripple suppression is only marginally littered with the professionaltection circuit, since the enter is already neatly stabilised by T1, however the current via D1 does go with the flow in the direction of the output. The presence of C2 should even be taken into account.

In this circuit, with an adjustable voltage regulator one of theses the LM317 and an output voltage greater than 40 V, C2 will cause the voltage to be in brief larger than 40 V in the experience of a brief circuit, which can additionally result in the IC to be damaged. In that case, it'll be important to discover a completely different solution or use a distinct type of voltage regulator.